Dr Callahan discovered that toxins play a role in many psychological and physical problems. However, the toxins of TFT are not the same as the toxins of conventional medicine. In TFT a toxin is a normally harmless substance which has an adverse effect on the body's energy system. These include certain foods like wheat, milk, corn, eggs, sugar and coffee and inhaled substances like perfume and aftershave. However, toxin sensitivity is an individual thing. What is toxic for one individual may be no problem for another — 'One man's meat is another's poison'. Toxins have three effects in TFT: they can make a problem return after a successful treatment; they can prevent TFT or indeed any other form of therapy from working; and in some cases it is likely the toxin caused the problem. For example, many cases of insomnia are caused by toxins and panic attacks are often triggered by them. TFT Voice Technology™ can be used to identify toxin sensitivities in a matter of seconds. As part of your treatment you may be advised to make dietary changes to get the maximum benefit from your therapy. John highlights the importance of identifying any individual energy toxins in his book 'Unleash the Slim Within', a session of TFT Voice Technology™ is included as part of the 'Unleash the Slim Within' programme.